A process for the selective hydrogenation of C4-acetylenes in the presence of butadiene with the added benefit of extended catalyst stability has been developed.
Butadiene is an important starting material for the production of high molecular weight polymers and is used extensively to form synthetic rubber including styrene-butadiene rubber, nitrile-butadiene rubber, buna-S rubber, and trans-polybutadiene rubber, and adiponitrile and styrene butadiene latex in paints. Butadiene is usually a by-product from steam cracking naphtha. However, the product butadiene regularly contains impurities that must be removed before the butadiene may be used as a starting material. The principal impurities are acetylenes including ethylacetylene, methylacetylene and vinylacetylene. Historically, two approaches have been used to remove the acetylenes: extractive distillation using a solvent to selectively absorb the acetylenes, or selective hydrogenation of the acetylenes.
In using selective hydrogenation, copper-containing catalytic composites have been shown to be successful. Copper-containing catalytic composites used for selective hydrogenation of acetylenes are disclosed in U.S. Pat. No. 4,493,906 which discloses the catalyst as {fraction (1/16)} inch extrudates, U.S. Pat. No. 4,440,956 which discloses the catalysts as xe2x85x9 inch pellets, U.S. Pat. No. 3,912,789, U.S. Pat. No. 3,218,268 which disclose the catalysts as {fraction (3/16)} inch tablets, and U.S. Pat. No. 3,751,508 which disclose the catalysts as 3 mm tablets (about xe2x85x9 inch tablet). In contrast to this art, applicants have discovered that a copper-containing catalytic composite where at least 50 and preferably 70 weight percent of the copper and optionally one or more activator metals are dispersed on the outer 200 microns of the catalyst support. It is most preferred that the catalyst composite particles also have an average diameter of about {fraction (1/32)} inch (800 microns) or less. A microsphere catalyst is shown herein to have much improved stability and selectivity versus similar catalysts of about {fraction (1/16)} inch (1600 microns) diameter.
The present invention is related to a process for selectively hydrogenating C4-acetylenes in a liquid hydrocarbon stream containing largely butadiene with the benefit of increased catalyst stability. Hydrogen and the hydrocarbon stream are contacted with a catalytic composite comprising an inorganic oxide support having dispersed thereon finely divided copper metal and optionally an activator metal selected from the group consisting of nickel, cobalt, platinum, palladium, manganese, and a combination thereof where at least 70 weight percent of the copper metal and the activator metal are dispersed on the outer 200 micron layer of the support. In a specific embodiment of the invention, at least 80 weight percent of the copper metal is dispersed on the outer 200 micron layer of the support. In another specific embodiment of the invention, hydrogen and the hydrocarbon stream are contacted with a catalytic composite comprising an inorganic oxide support having dispersed thereon finely divided copper metal and optionally an activator metal selected from the group consisting of nickel, cobalt, platinum, palladium, manganese wherein the catalytic composite is spherical and has an average diameter of about {fraction (1/32)} inch (800 microns) or less.